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SubjectRe: Linux 2.4.19pre1-ac1
Date
Hi Alan!

> > Will try this now, sounds possible - but does patch really use shared
> > memory? I will try to narrow it down a bit. There also were some changes
> > to mm/memory.c between 2.4.18-rc2-ac2 and 2.4.18-ac1. Also a possibility?
>
> Could be - as far as I can tell they are also in vanilla 2.4.18 (the
> ptrace ones)

The changes I see here between them do not seem to be related to ptrace. But
I think I already found one possible glitch by manual inspection there. Both
kernels are compiling just now so I can test later.

diff -u -r linux-2.4.18-rc2-ac2/mm/memory.c linux-2.4.18-ac1/mm/memory.c
--- linux-2.4.18-rc2-ac2/mm/memory.c Thu Feb 28 01:01:51 2002
+++ linux-2.4.18-ac1/mm/memory.c Thu Feb 28 00:54:09 2002
@@ -180,7 +180,7 @@
pgd_t * src_pgd, * dst_pgd;
unsigned long address = vma->vm_start;
unsigned long end = vma->vm_end;
- unsigned long cow = (vma->vm_flags & (VM_SHARED | VM_WRITE)) ==
VM_WRITE;
+ unsigned long cow = (vma->vm_flags & (VM_SHARED | VM_MAYWRITE)) ==
VM_MAYWRITE;

src_pgd = pgd_offset(src, address)-1;
dst_pgd = pgd_offset(dst, address)-1;
@@ -250,7 +250,7 @@
goto cont_copy_pte_range;

/* If it's a COW mapping, write protect it
both in the parent and the child */
- if (cow) {
+ if (cow && pte_write(pte)) {
ptep_set_wrprotect(src_pte);
pte = *src_pte;
}
@@ -460,21 +460,24 @@
int get_user_pages(struct task_struct *tsk, struct mm_struct *mm, unsigned
long start,
int len, int write, int force, struct page **pages, struct
vm_area_struct **vmas)
{
- int i = 0;
+ int i;
+ unsigned int flags;
+
+ /*
+ * Require read or write permissions.
+ * If 'force' is set, we only require the "MAY" flags.
+ */
+ flags = write ? (VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD);
+ flags &= force ? (VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE);
+ i = 0;

do {
struct vm_area_struct * vma;

vma = find_extend_vma(mm, start);

- if ( !vma ||
- (pages && vma->vm_flags & VM_IO) ||
- (!force &&
- ((write && (!(vma->vm_flags & VM_WRITE))) ||
- (!write && (!(vma->vm_flags & VM_READ))) ) )) {
- if (i) return i;
- return -EFAULT;
- }
+ if ( !vma || (pages && vma->vm_flags & VM_IO) || !(flags &
vma->vm_flags) )
+ return i ? : -EFAULT;
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ <- This looks somewhat bogus,
shouldn't it be "return i ? i : -EFAULT;" instead?

Greetings,
Andreas
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